1. Field of the Invention
The present invention relates to a light intensity distribution simulation method for obtaining a distribution of light intensity on a substrate surface at a time of exposure in the lithography process and computer program product.
2. Description of Related Art
For miniaturization of a pattern formed on a wafer, it is attempted to increase a numerical aperture NA of an exposure apparatus used for pattern forming. Therefore, an incident angle of light to a photomask and a wafer has been more increased. The incident angle of light especially to a surface of the photomask is so increased as to affect the pattern forming unfavorably.
The photomask comprises a pattern film having a film thickness such as a light shielding portion or a phase shifter portion. Because of a sidewall of the pattern film, a part which is not irradiated with the light generates in an aperture of the photomask. As a result, there arises a problem called shadowing in which an effective aperture ratio of the photomask fluctuates.
In consideration of the problem, in order to predict a pattern formed on a wafer according to a simulation, it is necessary to calculate the light diffraction phenomena generated in the aperture strictly based on a three-dimensional structure of a photomask. However, the calculation of diffraction phenomena based on the three-dimensional structure takes an immense time even with a high performance computer (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 7-29813).